Improved cascade apparatus

ABSTRACT

Improved cascade apparatus for developing electrostatic images wherein a latent electrostatic image supported on a moving member is developed by cascading a flow of developer material including a magnetic component and an electroscopic component through a development zone. A chute receives a sufficient quantity of the developer material from a conveyor which moves the developer material in buckets from a sump and unloads a developer material at the inlet side of the chute. A magnetic member is positioned at the inlet side of the chute in close proximity to the path of the conveyor to affect the buildup of the magnetic developer material in the path of the conveyor buckets such that a sufficient quantity of the developer material is directed along the chute into the development zone instead of a certain portion being returneed into the sump as the buckets are inverted by their movement to dump the conveyed developer at the inlet of the chute leading into the development zone.

United States Patent Hewitt 211 Appl. No.: 110,488

[52] US. Cl ..ll8/637, ll7/17.5, 118/636 [51] Int. Cl. ..G03g 13/00 [58]Field of Search ..1 18/637, 636, DIG. 24;

[56] i References Cited UNITED STATES PATENTS 3,4l5,224 12/1968 Hudson..1 18/637 3,105,770 10/1963 Lehmann et a1. ....1 18/637 3,303,8172/1967 Cranch et a1. ....l18/637 3,117,891 1/1964 Lehmann ..-.1l8/637Primary Examiner-Mervin Stein Assistant Examiner-Leo MillsteinAttorney-James J. Ralabate, Norman E. Schrader and Melvin A. Klein 1June6, 1972 57 ABSTRACT Improved cascade apparatus for developingelectrostatic images wherein a latent electrostatic image supported on amoving member is developed by cascading a flow of developer materialincluding a magnetic component and an electroscopic component through adevelopment zone. A chute receives a sufficient quantity of thedeveloper material from a conveyor which moves the developer material inbuckets from a sump and unloads a developer material at the inlet sideof the chute. A magnetic member is positioned at the inlet side of thechute in close proximity to the path of the conveyor to affect thebuildup of the magnetic developer material in the path of the conveyorbuckets such that a sufficient quantity of the developer material isdirected along the chute into the development zone instead of a certainportion being returneed into the sump as the buckets are inverted bytheir movement to dump the conveyed developer at the inlet of the chuteleading into the development zone.

3 Claims, 3 Drawing Figures PATENTUJUH 6 m2 SHEET 1 OF 2 INVENTOR.ROBERT E. HEWITT it A Q ATTORNEY 1' CASCADE APPARATUS This inventionrelates to an improved cascade development apparatus which increases theflow of developer material unloaded from a bucket conveyor to anentrance chute leading to a cascade development zone for a moreefficient development.

In the process of xerography as described, for example, in U.S. Pat. No.2,297,691 to Chester F. Carlson, a xerographic plate formed of aconductive backing material upon which is placed a. conductiveinsulating material is charged uniformly in the surface of the placeexposed to a light image of an original to be reproduced. Thephotoconductive coating is caused to become conductive under theinfluence of the light image so as to selectively dissipate theelectrostatic charge found thereon thus producing an electrostaticlatent image. The latent image is then developed by means of a varietyof finely divided pigmented resins which have been specificallydeveloped for this purpose. The pigmented resin material or toner iselectrostatically attracted to the latent image on the photoconductivesurface in proportion to the ion charge found thereon that is areas ofsmall charge concentration become areas of low toner density while areasof greater charge concentration become proportionately more dense, thefully developed images generally transferred to a support material, asfor example, paper and the image fixed thereto to form a permanentrecord of the original document.

One of the most widely used methods of developing a latent electrostaticimage is by means of cascade development in which a two componentdeveloper material is caused to flow down over the moving image bearingphotoconductive surface to effect image development. The toner andcarrier material are triboelectrically charged to opposite polaritiesand the particulate toner material adheres to the carrier in a chargedstate. As the toner laden carrier beads flow over the photoconductivesurface, the toner is electrostatically stripped from the carrier andattracted to the plate surface by the relatively stronger force fieldsassociated with the imaged areas. Cascade development has a highdevelopment latitude and is particularly noteworthy in freedom frombackground deposition. Further, the process is dependable and operateswith high efficiency under extreme humidity conditions and is easilyconverted to give either positive or reverse reproduction of theoriginal document to be copied.

There are, however, certain problems which may result with cascadedevelopment, as for example, solid areas and tonal patterns may notdevelop well especially if the proper mixture of carrier to toner is notmaintained as toner is consumed. Also, cascade development under certainconditions, such as high electrostatic contrast, may result in carrierbeads sticking to the photoconductive surface.

Heretofore efforts to develop electrostatic images by a techniquedifferent from cascade development has centered largely on magneticbrush development in which the granular carrier is selected which hasferromagnetic properties as well as having a triboelectric relationshipto impart the desired electrostatic property to the toner as in thecascade development. On inserting a magnet into such a mixture of tonerand magnetic granular material, the carrier particles align themselvesalong the lines of force of the magnet to assume a brushlike array withthe toner particles electrostatically coated on the surface of themagnetic carrier to affect the desired development as described, forexample, in US. Pat. No. 2,892,446 and US. Pat. No. 2,910,964. Whilemagnetic development is suitable for machine application, there arecertain disadvantages. Thus, in magnetic development, only part of thebrush contacts the xerographic surface. In addition, the magnetic fieldrestricts the motion of the carrier particles interferring with theindividual toner particles rolling across the image surface. As aconsequence of this, a higher concentration of toner is generallyessential in magnetic development.

A recent tendency has been to use a cascade development process fordevelopment of the electrostatic images using a high density developermaterial including a magnetic carrier component with the electroscopictoner component and it is the purpose of the present invention toimprove cascade development in this sense.

It is therefore an object of the invention to improve cascadedevelopment of electrostatic latent images.

It is another object of the invention to enable high print quality atvery high development speeds.

It is still another object of the invention to present developermaterial in a relatively high flow rate of a development zone.

It is still a further object of the present invention to transportdeveloper material from the sump portion of a developer housing to thedevelopment zone in a manner more efficient to heretofore.

It is still a further object of the present invention to directsubstantially all the developer material conveyed by a bucket conveyorassembly to a cascade development zone with a minimum of spillage.

These and other objects of the present invention are attained by meansof establishing a magnetic field in close proximity to the path of abucket conveyor in the area of the development zone such that developermaterial unloaded from the buckets is substantially directed along aninput chute to the cascade development rather than having spillage backinto the sump of the developer housing.

For a better understanding of the present invention as well as otherobjects and further features thereof reference is had to the followingdetailed description of the invention to be read in conjunction with theaccompanying drawings wherein:

FIG. 1 is a schematic side elevation of a continuous automaticxerographic reproducing machine having a cascade development zone andincorporating development apparatus constructed in accordance with theinstant invention;

' FIG. 2 is an enlarged partial sectional view of cascade developingapparatus without the present invention; and

FIG. 3 is an enlarged partial sectional view of cascade developingapparatus illustrating the features of the present invention.

Referring now to the drawings, there is shown in FIG. 1 an embodiment ofthe subject invention in a suitable environment such as an automaticxerographic reproducing machine employing a drum shaped xerographicplate 10 comprising a photoconductive layer which is placed on aconductive backing and is moved in an uphill direction in thedevelopment zone on a shaft 12 journaled in the machine frame. Therotation causes the plate surface to sequentially pass a series ofxerographic processing stations. For the purposes of the presentdisclosure, the several xerographic processing stations in the path ofmoving of the plate surface may be described functionally as follows:

A charging station A at which a uniform electrostatic charge isdeposited on the photoconductive plate;

An exposure station B at which light radiation pattern of copy to bereproduced is projected onto the plate surface, dissipate the charge inthe exposed areas thereof to thereby form a latent electrostatic imageof the copy to be reproduced;

A developing station C at which xerographic developing materialincluding electroscopic toner particles and a magnetic interiorcomponent is cascaded over the plate surface whereby the toner particlesadhere to the latent electrostatic image to form a toner powder image inthe configuration of the copy being reproduced in a manner as will bedescribed more fully hereinafter;

A transfer station D at which the toner powder image iselectrostatically transferred from the plate surface to a supportmaterial such as paper; and 4 A drum cleaning and discharge station E atwhich the plate surface is crushed to remove residual toner particlesremaining thereon after image transfer and exposed to a relativelybright light source to affect substantially complete discharge of anyresidual electrostatic charge remaining thereon.

For a more detailed description of the processing stations which havebeen only briefly described above, reference is made to copendingapplication Ser. No. 838,914 filed on July 3, 1969 and commonly assignedwith the instant application. In accordance with the present invention,the development station includes a conveyor assembly 14 for transportingdeveloper material from a sump 16 to an elevated location, The developermaterial comprises a mixture of any suitable magnetic carrier particlesand an electroscopic toner powder with the toner powder adhering to thecarrier particles as a result of the triboelectric effect. Typicalcarrier materials comprise powdered iron including the types knowncommercially as alcoholized iron and carboxal iron, steel nickel, alloysof magnetic iron such as nickel-iron alloys, nickel-colbalt iron alloys,and magnetic oxides, such as iron oxide, hematite R and magnetite (Fe Oand ferromagnetic ferrites.

Where the ferromagnetic material does not have the desired triboelectricrelationship to the toner, the ferromagnetic material may be used as acore covered with a resinous coating having the desired triboelectricproperties as described, for example, in U.S. Pat. No. 2,618,551 toWalkup and U.S. Pat. No. 2,874,063 to Greog. Typical electroscopic tonerpowders are described in U.S. Pat. No. 2,618,551 to Walkup, U.S. Pat.No. 2,618,552 to Wise, and U.S. Pat. No. 2,638,416 to Walkup and Wise.

The conveyor assembly 14 includes a plurality of buckets stapled orotherwise suitably secured to endless belts 22 mounted on upper pulleys24 and lower pulleys 26 for move ment in a path of travel indicated bythe arrow, The lowermost pulleys are located so that the buckets canpass through a sump of development material beneath the cascadedevelopment zone 28. The sump is continually reloaded with developerfalling from the cascade development zone and captured and directed by apickoff baffle 30.

Above the development zone is an input chute 32 receiving the conveyeddeveloper material as it is unloaded or dumped from the buckets andgravity dropped for cascading through the development zone. Due to thefact that toner particles are lost from the development system throughthe development of the electrostatic images on the xerographic drum, atoner dispenser 36 is employed to supplement that toner consumed fromthe system.

What would normally result in the case of a cascade development systemin the absence of the instant invention is illustrated in FIG. 2. Asshown in this Figure, the developer material carried by the bucketsupwardly at a slight angle with respect to the vertical are then movedaround the upper reaches of the upper pulleys 24 causing the bucketssequentially to tip and then dump the developer material toward theinput chute 32. As a consequence of this, some of the developer materialis caused to fall back into the sump through a gap 35 thereby detractingfrom the flow of developer material presented to the development zone.

In order to alleviate this situation and improve cascade development ofthe electrostatic latent images by presenting sufiicient developermaterial in the development zone, a magnetic field is established acrossthe gap 35 through which the buckets 20 of the conveyor are passed suchthat developer spillage from the buckets 20 as they are tipped is pulledinto the magnetic field to form a bridge 40 across the gap. The magneticfield is effected by positioning a magnet member 50 on the lower surfaceof the inlet side of chute 32 adjacent to the gap 35. In this manner,substantially all of the developer material unloaded from the buckets isdirected onto the chute and is prevented from falling into the sump areathereby increasing the flow of the developer material being conveyed bythe bucket conveyor to the development zone. If, in fact, contact ismade by the edge of the buckets with bridge 40 formed with the developermaterial, the bridge will be peeled away sufi'iciently for the desiredclearance but will quickly reform as additional developer material isunloaded from succeeding buckets.

While the present invention as to its ob ects and advantages have beendescribed as carried out in the specific embodiment thereof, it is notintended to be so limited but is intended to be protected broadly withinthe scope of the appended claims.

What is claimed is:

1. Apparatus for use in a cascade developing station wherein a latentelectrostatic image supported on a moving member is developed by a flowof developer material including a magnetic component and anelectroscopic component moving through a development zone, theimprovement comprising a housing including a sump portion containingdeveloper material including a magnetic component and an electroscopiccomponent for developing electrostatic images, chute means disposed inthe housing for receiving a predetermined quantity of the developermaterial and directing the flow of the developer material onto a latentelectrostatic image moving through a development zone,

conveyor means including buckets for loading developer material from thesump portion and unloading the developer material onto the chute means,and

magnetic field producing means positioned on the inlet side of saidchute means and coextensive therewith in close proximity to the path ofsaid conveyor means to effect a buildup of the developer materialtherebetween whereby any gap between the chute means and conveyor meansis minimized and sufficient developer material is directed along saidchute means towards the development zone.

2. The apparatus of claim 1 wherein said magnetic field producing meanscomprises a magnet member with pole faces oriented at right angles tothe surface ofthe chute means.

3. Apparatus according to claim 2 wherein the magnitude of the magneticfield producing means is sufficient to effect rapid accumulation of thedeveloper material on the chute means in the path of the conveyor means.

2. The apparatus of claim 1 wherein said magnetic field producing meanscomprises a magnet member with pole faces oriented at right angles tothe surface of the chute means.
 3. Apparatus according to claim 2wherein the magnitude of the magnetic field producing means issufficient to effect rapid accumulation of the developer material on thechute means in the path of the conveyor means.